1. Field of the Invention
The present invention relates to a pulse wave radar device that uses a pulse wave. More specifically, it relates to an in-vehicle pulse wave radar device that prevents mistaken measurement of a pulse wave sent from any other radar device and utilizes the pulse wave radar device to enable communication.
2. Description of the Related Art
A variety of types of pulse wave radar devices are known which measure a distance to a target based on a lapse of time that has elapsed from a moment of transmission of a pulse wave to a moment of reception of a reflection from the target. With such a pulse wave radar device, a lapse of time that has elapsed from a moment of emission of a transmitting wave to a moment of reception of a receiving wave is measured to thereby obtain a signal that is proportional to a distance from the pulse wave radar device to a target, according to which signal, the distance is calculated.
A pulse wave radar device and the like for use in weather observation aimed at long-range measurement provides an antenna itself with sharp directivity and so scarcely interferes with any other pulse wave radar device in radio communication. An in-vehicle pulse wave radar device and the like aimed at short-range measurement, on the other hand, provides it with wide directivity and so may be impossible to distinguish between a transmitting wave of its own and that of any other device in a case where a number of pulse wave radar devices are present in the same area.
Therefore, various types of radar devices have been developed to enable distinguishing between a transmitting wave of one of the devices and that of any other even if a number of pulse wave radar devices are present in the same area (see, for example, Japanese Patent Application Laid-Open No. 2002-277541).
The following will describe a conventional pulse wave radar device with reference to FIGS. 1 and 2. FIG. 1 is an explanatory block diagram of a configuration of the conventional pulse wave radar device. In FIG. 1, a reference numeral 81 indicates an information encoder for generating a code string obtained by encoding an identifier and an identification number that are used to identify a pulse wave radar device, a reference numeral 82 indicates a transmitter for phase-modulating an information pulse and transmitting it, a reference numeral 84 indicates an antenna for emitting a transmitting wave and receiving a receiving wave, a reference numeral 85 indicates a receiver for receiving a receiving wave, a reference numeral 86 indicates a phase detector for detecting a receiving wave, a reference number 87 indicates an A/D converter for digitizing detected information, and a reference numeral 88 indicates a signal processor for collating information digitized by the A/D converter with a code string obtained by encoding an identifier and an identification number by the information encoder 81 and, only if they agree, measuring a difference in time from a reference pulse to thereby calculate a distance to a target.
FIG. 2 is a timing chart of an input signal to the signal processor 88 for explaining operations of the conventional pulse wave radar device. The signal processor 88 compares between an identifier and an identification number that are received and those that are transmitted. In a case where the transmitted identifier and identification number are represented as code string “a”, if the received identifier and identification number constitute the code string “a”, the processor measures a delay time between the transmitted wave and the received wave, thereby calculating a distance to the target. If the received identifier and identification number constitute code string “b”, the processor abandons information of the measured delay time utilizing that code string.
With such a pulse wave radar device, if a plurality of targets is present as shown in FIG. 2, receiving waves are multiplexed one on another, so that it is impossible to compare the identifier and identification number that are received with those that are transmitted. Further, the received code string is compared or correlated, so that a high-speed signal processing circuit is required, thus leading to an increase in power consumption.